1. Field of the Invention
This invention relates to a hub drive, in particular a wheel hub drive, with a stationary hub carrier, a rotating hub, a hydrostatic axial piston motor utilizing the swashplate construction fastened to the hub carrier and connected in a direct drive connection with the hub, and with a brake that is connected directly between the hub carrier and the hub.
2. Background Information
One fundamental problem with hub drives is that the space available is generally limited. For example, when the hub drive is used as a wheel hub drive, it must be installed inside the wheel rim. A hub drive of the prior art is described in DE-OS 24 07 274, in which the bearing system of the motor shaft of the axial piston motor is simultaneously the bearing system of the rotating hub. In this arrangement, the common bearing of the hub, as well as the motor shaft, must be designed so that they are large enough and strong enough to withstand the external loads and propulsion forces (transverse forces) that will be exerted on the hub. It is therefore necessary to make the motor shaft and bearing system very large and strong to keep the bending loads low.
The object of this invention is to make available a hub drive of the type described above that has the most compact dimensions possible, in particular in the radial direction, as well as high power density, and one that can be manufactured easily and economically.
The invention provides an axial piston motor with an external bearing cylinder block and a motor shaft in the form of a torquing adapter that is free of lateral forces and is coupled rotationally synchronously with the hub, and that the hub has a separate bearing system in the hub carrier.
The motor shaft of the axial piston motor is kept free of the transverse forces exerted both by the propulsion system and external loads, which thereby makes it possible to minimize its diameter. For this purpose, the motor shaft is in the form of a torquing adapter that is free of lateral forces. Accordingly, the cylinder block is not mounted on the motor shaft but in the motor housing, which is called an external bearing system in contrast with an internal bearing system on the motor shaft. The hub is provided with a separate hub bearing system. Because the brake is connected directly between the hub and the hub carrier, the motor shaft does not need to absorb any torsion forces that are caused by the braking moment that is generated during braking. The motor shaft need only absorb the output moment that is delivered by the axial piston motor.
The hub can be mounted on or in the hub carrier. In one embodiment of the invention, the hub has a central bearing journal which is located radially inside a bearing segment that is connected with or is formed on the hub carrier. The hub bearing system is provided radially between the bearing journal and the bearing segment, and the brake is located radially outside the hub bearing system. This construction provides the largest possible diameter of the brake, so that large braking forces can be generated in spite of the compact dimensions of the hub drive of the invention.
The bearing system may consist of two helical roller bearings, in particular two conical roller bearings in an O-arrangement, so that the hub drive can absorb high radial loads. The helical roller bearings may be biased by means of a shaft nut that is located on the bearing journal.
In one refinement of the invention, the brake is located axially in the vicinity of the bearing system, so that compact dimensions are also achieved in the axial direction.
The goal of small dimensions of the hub drive is also achieved by a rotationally synchronous coupling between the hub and the motor shaft. The motor shaft is inserted into a central boring of the bearing journal and is provided with longitudinal gearing that is effectively engaged with longitudinal gearing in the boring (a spline type connection is provided).
If the hub has a flange for the fastening of at least one wheel rim, the hub drive of the invention can be used as a wheel hub drive. In this case, it is advantageous in terms of reducing the time, effort and expense involved in the manufacture of the hub if the flange and the bearing journal are made in one piece with each other. Additional advantages may be achieved by having the hub include a rim centering device and having the flange include fastening borings. The location of the brake in the hub drive of the invention is achieved in a simple manner because the flange has a companion drum that covers and engages with the brake.
It is also advantageous if the companion drum is detachably connected with the flange. In one embodiment, this type of fastening can be achieved by fixing the companion drum in its axial position by wheel fastening bolts. The wheel fastening bolts and/or longitudinal gearing on the outer peripheral area of the flange and longitudinal gearing on the inner peripheral surface of the companion drum (a spline connection) may transmit the braking moment between the companion drum and the flange.
The brake may be a hydraulically actuated spring-loaded multiple-disc brake, and in particular a wet brake. If a brake of this type is connected to the oil circulation system of the axial piston motor, the cooling and filtering devices of the hydrostatic circuit can also be used. The brake is therefore capable of a high braking power.
In this context it is advantageous if, radially between a terminal segment of the companion drum and the hub carrier, there is a sealing element, in particular a shaft gasket. When this shaft gasket becomes worn, it can be replaced easily by removing the companion drum.
The hub drive of the invention can be easily fastened to a vehicle if the hub carrier is provided with a fastening flange.
In one refinement of the invention, the axial piston motor is located inside the hub carrier to save space. In one embodiment of the invention, the hub carrier forms a motor housing for the axial piston motor. A separate motor housing is therefore unnecessary, which reduces the amount of space required. Further, if all the space available is used, the axial piston motor can be realized so that it has greater power.
If the hub carrier, on its end opposite the bearing segment, has a removable cover which is realized in the form of the control base receptacle of the axial piston motor, the space conditions are favorable for the connections of the hydraulic lines to the axial piston motor.
The hub drive of the invention provides that the swashplate can be removed from the hub carrier thereby providing easy installation and removal of the hub drive.
In a second embodiment of the invention, the hub carrier forms a support housing to hold a motor housing of the axial piston motor, whereby the motor housing is fastened in the hub carrier by torque-transmitting and vibration-reducing means that are located radially between the motor housing and the hub carrier. Torque-transmitting and vibration-reducing means are connected to the motor shaft. This hub drive of the invention makes it possible, by isolating the structure-borne noises to prevent or at least reduce the transmission of structure-borne noises. This internal acoustical isolation of the axial piston motor consists of the noise-damping fastening of the motor housing in the hub carrier and of the additional (internal and/or external) isolation of the motor shaft. This construction does not occupy any additional space as compared to acoustical insulation measures that encapsulate the hub drive. The torque-transmitting and vibration-reducing means consist of an elastomer, a combination of elastomers, one or more non-ferrous metals, plastic or a combination of plastics. Combinations of these different types of materials can also be used. An essential teaching of the invention is the interruption or reduction of the transmission of structure-borne noise by the use of intermediate components that have a different modulus of elasticity. Suitable materials or combinations of materials can then be selected depending on the damping properties desired.
In one embodiment of the hub drive of the invention, the axial motor is a fixed displacement motor.